People reported a bug on a high end server with many pcie devices, where kernel bootup with crashkernel=384M, and kaslr is enabled. Even though we still see much memory under 896 MB, the finding still failed intermittently. Because currently we can only find region under 896 MB, if w/0 ',high' specified. Then KASLR breaks 896 MB into several parts randomly, and crashkernel reservation need be aligned to 128 MB, that's why failure is found. It raises confusion to the end user that sometimes crashkernel=X works while sometimes fails. If want to make it succeed, customer can change kernel option to "crashkernel=384M, high". Just this give "crashkernel=xx@yy" a very limited space to behave even though its grammer looks more generic. And we can't answer questions raised from customer that confidently: 1) why it doesn't succeed to reserve 896 MB; 2) what's wrong with memory region under 4G; 3) why I have to add ',high', I only require 384 MB, not 3840 MB. This patch tries to get memory region from 896 MB firstly, then [896MB,4G], finally above 4G. Dave Young sent the original post, and I just re-post it with commit log improvement as his requirement. http://lists.infradead.org/pipermail/kexec/2017-October/019571.html There was an old discussion below (previously posted by Chao Wang): https://lkml.org/lkml/2013/10/15/601 Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx> Cc: Dave Young <dyoung@xxxxxxxxxx> Cc: Baoquan He <bhe@xxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: yinghai@xxxxxxxxxx, Cc: vgoyal@xxxxxxxxxx --- v5 -> v6 discard bottom-up allocation, just repost dyoung's original patch with commit log improved --- arch/x86/kernel/setup.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c index 3d872a5..fa62c81 100644 --- a/arch/x86/kernel/setup.c +++ b/arch/x86/kernel/setup.c @@ -551,6 +551,22 @@ static void __init reserve_crashkernel(void) high ? CRASH_ADDR_HIGH_MAX : CRASH_ADDR_LOW_MAX, crash_size, CRASH_ALIGN); +#ifdef CONFIG_X86_64 + /* + * crashkernel=X reserve below 896M fails? Try below 4G + */ + if (!high && !crash_base) + crash_base = memblock_find_in_range(CRASH_ALIGN, + (1ULL << 32), + crash_size, CRASH_ALIGN); + /* + * crashkernel=X reserve below 4G fails? Try MAXMEM + */ + if (!high && !crash_base) + crash_base = memblock_find_in_range(CRASH_ALIGN, + CRASH_ADDR_HIGH_MAX, + crash_size, CRASH_ALIGN); +#endif if (!crash_base) { pr_info("crashkernel reservation failed - No suitable area found.\n"); return; -- 2.7.4 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
